Potential for Downdip Extension of the Travis Peak Gas Play, West Margin of the East Texas Basin

As U.S. conventional natural gas resources are depleted, resources in low-permeability (tight) sandstone are increasingly important to domestic gas supply, and their importance will increase worldwide in future decades. Travis Peak (TP) tight sandstones have produced gas since the 1940s. From 1961 through 2005, TP cumulative gas production along the west margin of the East Texas basin was 1.43 Tcf from fluvial-deltaic sandstones. The objective of this study was to assess the potential for basinward (southeastward) extension of TP production from the west margin of the basin.

We evaluated structural and stratigraphic settings of the TP formation in an 11-county area, using five regional 2-D seismic lines and 860 well logs. Along the west margin of the East Texas basin, TP gas is produced from southeast-trending sandstones that were deposited by the Ancestral Red River fluvial-deltaic system. In the downdip study area, TP sandstones were deposited in fluvial-deltaic, shelf, slope, and deepwater environments.

Drilling mud densities suggest that strata deeper than 12,500 ft may be overpressured, and the geothermal gradient (1.6 oF/100 ft) indicates that this overpressure may be relict, resulting from hydrocarbon generation by source rocks of the Smackover and Bossier formations. Faults associated with Louann Salt deformation extend from the Smackover and Bossier formations to the TP formation, providing gas-migration pathways.

Along the west margin of the East Texas basin, TP gas is produced from structural, stratigraphic, and combination traps. Because there are few downdip well logs and seismic lines, our ability to identify specific structural or stratigraphic traps in this region was limited. However, several potential downdip hydrocarbon plays noted include (1) updip pinch-outs of fluvial, deltaic, slope and fan sandstones, (2) pinch-outs of deltaic sandstones below a TP unconformity (3) sandstone pinch-outs at margins of salt-withdrawal basins, and (4) traps associated with salt structures.